The present invention is directed to control devices for bicycle transmissions and, more particularly, to an apparatus that facilitates the gear shifting operation for the transmission.
Bicycle transmissions known in the art include internal transmissions housed within the rear hub and external transmissions mounted on the rear hub around the crank spindle. Internal transmissions typically employ a planetary gear device and a clutch for selecting different power transmission paths through the planetary gear device. Such transmissions include the pushrod type and the rotary cam type. The pushrod type internal transmission comprises a pushrod slidingly mounted in the axial direction through the center of the hub spindle for moving the clutch axially to select the plurality of power transmission paths through the planetary gear device. A rotary cam type internal transmission includes a cam shaft with a plurality of cams arrayed in the axial direction, wherein the cam shaft is mounted for rotation around the hub spindle between the sun gears of the planetary gear device and the hub spindle. The rotational position of the cam shaft determines which sun gears are nonrotatably fixed to the hub spindle and which sun gears are free to rotate around the hub spindle. This, in turn, determines the power transmission path through the planetary gear device. External transmissions typically comprise a plurality of coaxially arranged sprockets that rotate with the pedals and/or the rear wheel and a corresponding front and/or rear derailleur for shifting a chain among the corresponding plurality of sprockets as the bicycle is being pedaled.
In both types of transmissions, a shift control device attached to the handlebar, for example, is coupled to the transmission by means of a control cable having an inner wire that slides within an outer casing. Operating the shift control device in one direction causes displacement of the inner wire towards the shift control device, while moving the shift control device in the another direction causes displacement of the inner wire towards the transmission by means of a return spring provided to the shift control device or to the transmission.
With an internal transmission, pedaling the bicycle causes substantial contact forces to be generated among the components that make up the planetary gear device. Thus, unless essentially no power is being transmitted to the rear wheel, such as when the rider stops pedaling or when the pedals are situated at the top or bottom deadpoint, the shifting operation will require the application of considerable force to the pushrod or cam shaft. When the shifting operation includes displacement of the inner wire towards the transmission by means of the return spring provided to the shift control device or to the transmission, very often the return spring is incapable of providing the required force until the pedals are situated at the top or bottom deadpoint or until the rider stops pedaling.
With an external transmission, the bicycle must be pedaled in order to shift the transmission. Thus, optimum shifting occurs either when the pedals are situated at the top or bottom deadpoint or when the rider consciously reduces the pedaling force.
The present invention is directed to a shift assist apparatus which helps to reduce the force applied to the transmission when a shifting operation is desired. In one embodiment of the present invention, a control apparatus for controlling a drive member rotatably supported on a bicycle includes a mounting member for mounting the apparatus to the bicycle, a braking mechanism coupled to the mounting member for applying a braking force to the drive member; and a coupling mechanism adapted to couple the braking mechanism to a shift control mechanism so that the braking mechanism applies the braking force to the drive member upon actuation of the shift control mechanism.
In a specific embodiment of the present invention, the apparatus includes a mounting member for mounting the apparatus to the bicycle; a rotary member rotatably supported to the mounting member; a first braking member; a first cam member coupled to the mounting member; a second cam member coupled to the rotary member for rotation therewith; wherein at least one of the first cam member and the second cam member moves the first braking member when the first cam member and the second cam member rotate relative to each other; a coupling pawl coupled to the rotary member; a pawl biasing member for biasing the coupling pawl toward a coupled position for coupling the rotary member for rotation with the drive member; and a pawl control member for retaining the coupling pawl in a decoupled position. In this embodiment, the pawl control member is adapted to couple to a shift control mechanism so that the coupling pawl is allowed to move toward the coupled position upon actuation of the shift control mechanism.